1. Field of the Invention
The present invention relates to a surface acoustic wave device including a quartz substrate, and more particularly to a surface acoustic wave device which is formed by laminating a piezoelectric thin film on a quartz substrate and is adapted to generate a newly discovered higher order mode of leakage elastic surface acoustic waves.
2. Description of the Related Art
Heretofore, surface acoustic wave devices have been widely used as, e.g., band-pass filters in mobile communication equipment. The surface acoustic wave device has a structure including at least one interdigital transducer (IDT) comprising at least one pair of comb electrodes disposed in contact with a piezoelectric substance. Such a surface acoustic wave device has been used in various application forms such as resonators and delay lines, in addition to band-pass filters.
As substrate materials of surface acoustic wave devices, there are known piezoelectric single crystals such as LiNbO.sub.3, LiTaO.sub.3 and quartz. A structure including an IDT disposed on a substrate made of any one of those materials to generate Rayleigh waves has been previously practiced.
Surface acoustic wave devices including quartz substrates have had the problem that, while the quartz substrate exhibits a good temperature characteristic, the Rayleigh waves which are surface acoustic waves generated by the quartz substrate have a low sonic speed.
Meanwhile, it is known that, in a surface acoustic wave device including a quartz substrate, leakage elastic surface acoustic waves are generated in addition to the Rayleigh waves and the sonic speed of these leakage elastic surface acoustic waves are relatively high compared to the sonic speed of the Rayleigh waves. However, the leakage elastic surface acoustic waves are attenuated to a large extent during transmission. This attenuation is due to the fact that the leakage elastic surface acoustic waves have a decay constant which causes the leakage elastic surface acoustic waves to decay and be attenuated. For this reason, it has been difficult to prevent attenuation and make practical use of the leakage elastic surface acoustic waves.
Thus, despite exhibiting a good temperature characteristic, quartz substrates have not been previously used as materials for surface acoustic wave devices required to operate at a relatively higher frequency, because of the low sonic speed of Rayleigh waves, and difficulties preventing attenuation of elastic surface acoustic waves utilizing leakage elastic surface acoustic waves.